Rational Modeling of Nonhomogeneous Systems

Abstract

Nonhomogeneous transmission systems occur in several practical configurations such as nonideally transposed overhead lines, cross-bonded cables, and river crossings of overhead lines. In the past, a compact and efficient representation of nonhomogeneous system (NhS) was only possible in the frequency domain as the chain matrix (matrix transfer function) was used to obtain an equivalent nodal admittance matrix. Time-domain representation of a NhS demands explicit representation of each homogeneous section, thereby not being an efficient solution. This work proposes to represent nonhomogeneous systems using a rational approximation which allows for a compact and accurate time-domain realization. In this approach, we exploit the fact that a NhS can be seen as a particular case of a frequency-dependent network equivalent. The frequency dependence of the NhS is included via the rational modeling of the admittance matrix using the so-called Vector Fitting algorithm. Two test cases are considered to illustrate the gain of the proposed solution. The first one is the modeling of a nonideally transposed transmission line, and the second one is a case of river crossing. To asses the accuracy of the modeling, the results are compared against the ones obtained either using the Numerical Laplace Transform and PSCAD.